This invention relates to a surface-treated poly methyl silsesquioxane powder. More particularly, it relates to a surface-treated poly methyl silsesquioxane powder having a properly controlled contact static charge.
It is known that poly methyl silsesquioxane can be obtained by hydrolysis of a trifunctional silane, such as methyltrichlorosilane, followed by polycondensation. For example, Belgian Patent No. 572,412 teaches a method of obtaining solid poly methyl silsesquioxane by hydrolyzing methyltrichlorosilane in an atomized state, or by adding it dropwise to a large volume of water to effect hydrolysis. These methods, however, have a disadvantage that a considerable quantity of chlorine is left in the powder of poly methyl silsesquioxane formed. To solve this difficulty Japanese Patent Publication Kokai No. 54-72300 discloses a process in which a methyltrialkoxysilane and/or a partial hydrolyzate thereof is hydrolyzed in an aqueous solution of an alkaline earth metal hydroxide or an alkali metal carbonate to effect polycondensation.
Such a process is free of the aforementioned disadvantage, but poses a new problem that the powder of poly methyl silsesquioxane formed still contains considerable amounts of alkaline earth metal or alkali metal. In Japanese Patent Publication Kokai No. 60-13813, one of the inventors of the present invention proposes a process in which a methyltrialkoxysilane and/or a partial hydrolyzate thereof is hydrolyzed in an aqueous solution of an amine and/or ammonia to effect polycondensation, thereby giving a powder of poly methyl silsesquioxane free from the problems mentioned above and having excellent free-flowing property.
The powder of poly methyl silsesquioxane thus prepared has found uses as an additive for rubber and plastics to enhance their water resistance and lubricity, as an anti-blocking agent for powder, and as an additive for grease to render it thixotropic. Efforts are continued to obtain powder of poly methyl silsesquioxane with better performance qualities, such as more spherical and finer particles, in order to further broaden its application fields. One of the inventors of the present invention formerly carried out the hydrolysis/polycondensation reaction described in Japanese Patent Publication Kokai No. 60-13813 at the interface between the layer of methyl trialkoxysilane and/or its parial hydrolyzate and the aqueous layer of ammonia and/or amine solution, while stirring the mixture under a controlled condition. Thus the inventor succeeded in producing a powder of poly methyl silsesquioxane which comprises nearly spherical, independent particles having a narrow particle size distribution, and having a large negative contact charge.
The powder of poly methyl silsesquioxane thus prepared, because of its particle shape and the large negative contact charge, can be applied not only to conventional uses but also to other fields in which a sharp particle size distribution is required.
The excessively large negative contact charge, however, causes problems in some cases when this powder is used as an anti-blocking agent or anti-sagging agent for electrophotographic toners, or when it is used in admixture with other type of powders. When added to a positively charged toner, for example, it decreases the positive charge of the toner, thereby adversely affecting the toner deposition on the surface of photosensitive drum. This phenomenon leads to a development failure.
Japanese Patent Publication Kokoku No. 53-22447 discloses metal oxide powders treated with an aminosilane for an additive to electrophotographic toners. However, it takes a long time to incorporate such treated powders with a base resin for toner and carbon black, and the toner thus obtained tends to agglomerate. Further, the treated metal oxide powders do not give enough surface slip, when they are incorporated into a synthetic resin. Thus a powder free of such problems is desired.